Endothelial Cell-Astrocyte Interactions

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75690/1/j.1749-6632.1988.tb51417.x.pd

Insights into the high-energy γ-ray emission of Markarian 501 from extensive multifrequency observations in the Fermi era

We report on the γ-ray activity of the blazar Mrk 501 during the first 480 days of Fermi operation. We find that the average Large Area Telescope (LAT) γ-ray spectrum of Mrk 501 can be well described by a single power-law function with a photon index of 1.78 ± 0.03. While we observe relatively mild flux variations with the Fermi-LAT (within less than a factor of two), we detect remarkable spectral variability where the hardest observed spectral index within the LAT energy range is 1.52 ± 0.14, and the softest one is 2.51 ± 0.20. These unexpected spectral changes do not correlate with the measured flux variations above 0.3 GeV. In this paper, we also present the first results from the 4.5 month long multifrequency campaign (2009 March 15-August 1) on Mrk 501, which included the Very Long Baseline Array (VLBA), Swift, RXTE, MAGIC, and VERITAS, the F-GAMMA, GASP-WEBT, and other collaborations and instruments which provided excellent temporal and energy coverage of the source throughout the entire campaign. The extensive radio to TeV data set from this campaign provides us with the most detailed spectral energy distribution yet collected for this source during its relatively low activity. The average spectral energy distribution of Mrk 501 is well described by the standard one-zone synchrotron self-Compton (SSC) model. In the framework of this model, we find that the dominant emission region is characterized by a size ≲0.1 pc (comparable within a factor of few to the size of the partially resolved VLBA core at 15-43 GHz), and that the total jet power (≃1044 erg s-1) constitutes only a small fraction (∼10-3) of the Eddington luminosity. The energy distribution of the freshly accelerated radiating electrons required to fit the time-averaged data has a broken power-law form in the energy range 0.3 GeV-10 TeV, with spectral indices 2.2 and 2.7 below and above the break energy of 20 GeV. We argue that such a form is consistent with a scenario in which the bulk of the energy dissipation within the dominant emission zone of Mrk 501 is due to relativistic, proton-mediated shocks. We find that the ultrarelativistic electrons and mildly relativistic protons within the blazar zone, if comparable in number, are in approximate energy equipartition, with their energy dominating the jet magnetic field energy by about two orders of magnitude. © 2011. The American Astronomical Society

Regulatory Federalism and Workplace Safety: Evidence from OSHA Enforcement, 1981–1995

The Occupational Safety and Health Act (OSH Act) gives states the option to enforce federal occupational safety and health standards on their own instead of relying on the federal Occupational Health and Safety Administration (OSHA). This legislative provision provides an opportunity to analyze a homogenous set of regulatory standards enforced by heterogeneous agents engaged in interjurisdictional competition. This study finds important differences in the effectiveness of enforcement options measured by occupational mortality. State-administered OSHA programs are associated with fewer workplace fatalities than states regulated at the federal level. This finding is consistent with regulatory federalism and government-as-facilitator models of OSHA enforcement. Copyright Springer Science+Business Media, Inc. 2006OSHA, Workplace regulation, Federalism, D73, L51,

Agent Based Modeling and Adaptation to Climate Change

Agent based modeling is a technique for simulating complex systems that allows the modeler to investigate both the potential for and the sources of emergent properties: behaviors of the system quite different from the behavior of any of the elements within it. Problems well suited to investigation by agent based models are those with many people solving a similar problem where their individual responses to the problem influence the choices that others make, where new technologies may emerge to assist them solve the problem, and where social dilemmas exist. These features are inherent in many problems of adaptation to climate change. Agent based modeling can not predict the future of a complex adaptive system – no method of modeling can – but it can offer insights into the relationship between features of current systems and the range of possible future adaptations that will be likely in response to climate change. Zusammenfassung Die agentenbasierte Modellierung als Methode der Simulation komplexer Systeme ermöglicht die Analyse von Potentialen und Ursprüngen emergenter Eigenschaften, die nicht allein auf Basis des Verhaltens der Elemente des Systems erklärt werden können. Für agentenbasierte Modellansätze bieten sich insbesondere solche Probleme an, bei denen eine Vielzahl von sich wechselseitig beeinflussenden Individuen in die Lösung desselben Problems einbezogen sind. Zudem kann die Entstehung neuartiger Techniken sowie bestehende Umgangsformen mit sozialen Dilemmasituationen analysiert werden. Die Probleme der Anpassung an den Klimawandel zeichnen sich durch diese Kennzeichen aus. Zwar kann die agentenbasierte Modellierung die Zukunft eines komplexen adaptiven Systems ebenso wenig vorhersagen wie andere Modelle, doch kann sie Einsichten in die Beziehungen zwischen verschiedenen Eigenschaften dieser Systeme und in die möglichen zukünftigen Anpassungsmaßnahmen an den Klimawandel und deren Kosten liefern